Metal pickling process



252. COMPOSITIONS,

Patented Aug. 4, 1931 UNITED STATES l-AUHIIHUI PATENT OFFICE GEORGE L. MAGOUN AND DEAL H. TOMPKINS, OF NITRO, WEST VIRGINIA, ASSIGNORS TO THE RUBBER SERVICE LABORATORIES COMPANY, OF AKRON, OHIO, A CORPO- RATION OF OHIO METAL PICKLING PROCESS Application filed November 6, 1930. Serial No. 493,907.

The present invention relates to the cleaning and preservation of metallic surfaces, wherein the metal is in contact with a liquid of an acid nature. More particularly, the invention relates to the prevention of excessive pittin and embrittlement of a metal when sub ected to a pickling process by treatment with a dilute solution of a non-oxidizing acid.

Certain objects of the present invention are to prevent the acid pickle liquor from attacking clean portions of the surface of a metal; to obviate over-pickling, embrittlement and pitting of the articles treated; to minimize the amount of metal lost in pickling; to increase the efficiency of the pickling operation; to prolong the effective life of the pickling bath; and particularly to facilitate the pickling operation. Other and further objects of the invention will be apparent from the following description and accompanying examples.

In the art of pickling, the metal is treated with a dilute acid to remove oxides such as rust, scale, and other deposits, after which the metal is preferably washed with water and dipped into an alkaline bath to remove the last traces of free acid. The acid removes the rust and scale, but unfortunately, from the pickling standpoint, unless some agent to prevent such action is present, it attacks the cleaned metal itself thereby causing loss of metal and producing an evolution of hydrogen gas, which escapes into the air, carrying with it a fine spray of the acid liquor from the pickling bath and producing an atmosphere possessing corrosive properties and one which is injurious to health and damaging to equipment.

By the present invention, these objectionable features of the pickling process are substantially overcome or reduced to a minimum. To accomplish to as great an extent as possible the objects set forth in accordance with the present invention, there is a tliioureaand aii aldehyde-ammonia; that is, 5' product formed by first reacting an aldehyde with ammonia, then further reacting a thiourea therewith, and treating the product so obtained with an acid of any concentration necessary to produce chemical combination at the reaction temperature employed.

In the examples hereinafter set forth for carrying out the metal pickling process, conditions were imposed which duplicated, so far as possible, those commonly followed in commercial practice, so far as concerned acid concentrations and temperatures employed.

Test pieces of 30 gauge cold rolled tin plate steel stock, approximately 4" x 3 in dimension, were immersed in approximately 750 c. c. of a water solution of sulfuric acid containing approximately 6% by weight of 66 Be. acid to which had been added a small quantity of one of the preferred type of inhibitors. The loss in weight of the steel test pieces resulting from maintaining the strips in the pickle bath in the manner described for a definite period of time was then determined. The temperature of the pickling bath was maintained at from 83 to 84 C. For the acid concentration set forth, commercial practice is to pickle at approximately 66 to 88 C. The results so obtained were compared with similar tests wherein the steel pieces were subjected, un-

der the conditions set forth, to the action of an acid solution of the strength and for the time specified above, but containing no inhibitor.

One method whereby one of the preferred class of compounds, for example a sulfuric acid derivative of a reaction product of thiocarbanilide and acetaldehyde-ammonia, was prepared as follows:

Substantially two molecular proportions of acetaldehyde were dissolved in an organic solvent, for example, a quantity of ethyl alcohol equal to approximately three times the Weight of the acetaldehyde. Ammonia, preferably in the anhydrous condition, was passed thereinto until substantially two molecular proportions of the gas was absorbed as indicated by the increase in weight, while agitating and maintaining a temperature preferably not higher than 25 C. To the product thus formed, substantially one molecular proportion of thiocarbanilide was added and the mixture heated to and maintained at a refluxing temperature while agitating until the reaction was complete. The solvent employed, for example ethyl alcohol, was then removed preferably by distillation. The residual product thus formed, consisting of a thick viscous resin, was then treated with substamially one molecular proportion of sulfuric acid, preferably in the form of approximately 93% acid, and the product thus formed heated in a convenient manner, at a temperature preferably of substantially 100 to 110 C. for a period of approximately 24 hours. The final product thus formed was a hard, brittle resin which formed a fine powder when ground that was readily and completely soluble in a pickle liquor, as for example dilute sulfuric acid.

A sample of the product prepared as described above was incorporated in a pickling bath in the manner hereinbefore described. Thus, a steel test piece, 3" x 4 in dimension, cut from 30 gauge cold rolled tin plate stock, exposing approximately 24 square inches of surface and weighing 17.5105 grams, was found to lose but 0.0285 grams after 40 minutes pickling in 750 c. c. of a 6% sulfuric acid solution containing 0.07 grams of the inhibiting product hereinbefore described. A similar test piece weighing 18.2050 grams and treated in the same manner, but without the use of any inhibitor, lost 8.5350 grams. Thus it is shown that when the sulfuric acid derivative of the reaction product of thiocarbanilide and acetaldehyde-ammonia is employed as an inhibitor, the loss in weight per square inch of surface exposed corresponds to 0.00119 grams, whereas when no inhibitor is employed in the test described, the loss per square inch of surface exposed corresponds to 0.35600 grams. The loss in weight per square inch of surface exposed is only 0.33 percent as great by employing the inhibitor set forth as results if no inhibitor is employed in the pickling, process. A greater saving in metal losses results from the use of a large amountv of the inhibitor than that employed in the example. Moreover, the steel plates pickled in the presence of the inhibitor set forth are clean and not stained upon removal from the bath.

Other acid derivatives of a reaction product of a thiourea and an aldehyde-ammonia have been prepared in a manner analogous to that hereinbefore set forth and tested as inhibitors in a pickling bath in the manner hereinbefore described. Thus, the following products were so prepared and tested:

Compound A.Sulfuric acid derivatives of the reaction product of substantially one molecular proportion of thiocarbanilide and substantially two molecular proportions of butyraldehyde-ammonia.

Compound B.Sulfuric acid derivative of the reaction product of substantially one molecular proportion of thiocarbanilide and substantially two molecular proportions of crotonaldehyde-ammonia.

Compound C.Sulfuric acid derivative of the reaction product of substantially one molecular proportion of thiocarbanilide and substantially two molecular proportions of heptaldehyde-ammonia.

Compound D.Sulfuric acid derivative of the reaction product of substantially one molecular proportion of thiocarbanilide and substantially two molecular proportions of formaldehyde-ammonia.

Compou/nd E.-Sulfuric acid derivative of the reaction product of substantially one molecular proportion of thiocarbanilide and substantially two molecular proportions of alpha-ethyl-beta-propyl-acrolein ammonia.

Compound F .Sulfuric acid derivative of the reaction product of substantially one molecular proportion of thiourea and substantially two molecular proportions of acetaldehyde-ammonia.

Compound G.Sulfuric acid derivative of the reaction product of substantially one molecular proportion of di-ortho-tolyl-thiourea and substantially two molecular proportions of acetaldehyde-ammonia.

Compound H.Sulfuric acid derivative of the reaction product of substantially one molecular proportion of phenyl-ortho-tolylthiourea and substantially two molecular proportions of acetaldehyde-ammonia.

Compound 1.Sulfuric acid derivative of the reaction product of substantially one molecular proportion of mono-phenyl-thiourea and substantially two molecular proportions of acetaldehyde-ammonia.

Compound J .Sulfuric acid derivative of the reaction product of substantially one molecular proportion of phenyl-piperidyl- LULI UUI'II UUI l IUIU,

thiourea and substantially two molecular proportions of acetaldehyde-ammonia.

Compound K.Sulfuric acid derivative of the reaction product of substantially one molecular proportion of phenyl-alpha-naphthyl-thiourea and substantially two molecular proportions of acetaldehyde-ammonia.

Compound L.Hydrochloric acid derivative of the reaction product of substantially one molecular proportion of thiocarbanilide and substantially two molecular proportions of acetaldehyde-ammonia.

Compound M.-Phosphoric acid derivative of the reaction product of substantially one molecular proportion of thiocarbanilide and substantially two molecular proportions of acetaldehyde-ammonia.

Compound N.Acetic acid derivative of the reaction product of substantiallv one molecular proportion of thiocarbanilide and substantially two molecular proportions of acetaldehyde-ammonia.

Compound 0.Oxalic acid derivative of the reaction product of substantially one molecular proportion of thiocarbanilide and substantially two molecular proportions of acetaldehyde-ammonia.

The results of the tests obtained on immersing steel test strips of 30 gauge cold rolled tin plate stock, 3" x 4 in dimension, for 40 minutes in 750 c. c. of 6% by weight of 66 B. sulfuric acid at 83 C. in the presence of the indicated quantity of one of the above described inhibitors, are given in Table I.

Table I Weight Wei ht of Weight of Weight of loss in Inhibiting compound inhfifimr steel strip steel strip grams per employed em 10 before after sq. inch p 3 pickling pickling ofsurl'ace exposed gram grams grams grams Compound A 0. 07 18.0335 18.0005 0. 00137 Compound B 0. 0T 17. 8082 17. 7740 0. 00142 Compound C--. 0, 07 17. 9498 17. 9415 0. 00035 pound D 0. 07 17. 9415 17.9280 0. 00056 Compound E 0.07 17. 9370 17. 9070 0. 00125 Comp und F... 0.07 17. 3640 17. 3425 0. 00090 Compound G". 0.07 17.8335 17.8165 0.00071 Compound H 0.07 17. 3235 17. 306 0. 00072 Compound 1..-. 0.07 17.8165 17. 799 0. 00071 Compound J 0. 07 17. 0737 17. 0471 0.00111 Compound K. 0. 07 17. 9956 17.9700 0.00082 Compound L. 0.07 18. 6535 18. 6251 0.00118 Compound M 0.07 17. 7737 17. 7520 0, 00090 Compound I\ 0. 07 17. 8746 17. 8557 0.00079 Compound 0. 0.07 17. 9028 17. 8752 0.00115 None N one 18. 2050 9. 6700 0. 35600 It 1s thus apparent from the data set forth that the preferred class of materials constitutes an important and highly efiicacious group of inhibitors, as in all cases wherein one of the preferred inhibiting compounds was incorporated in the pickle liquid, there resulted a great saving in the loss in weight of the steel test strips as compared with that resulting when no inhibitor was employed.

It has further been found that other ratios of acid, thiourea and aldehyde-ammonia than those hereinbefore set forth may be reacted, and the reaction products so obtained employed as inhibitors. Thus, approximately one molecular proportion of the reaction product of substantiall one molecular proportion of thiocarbanili e and substantially two molecular proportions of acetaldehyde-ammonia has been reacted with substantially one and two-thirds molecular proportions of sulfuric acid. The

compound thus produced was incorporated in a pickle liquor in the manner hereinbefore described, the amount of inhibitor employed, the bath, and the size and grade of steel sheets used being the same as in the hereinbefore described tests. A steel sheet weighing 18.3820 grams was found after pickling 40 minutes to have lost but 0.0225 grams, or 0.00094 grams per s Haw of surfacemmmlie same stock weighing 18.2050 grams and treated in the same manner, but with no inhibitor present, suffered a loss of Silflgrams oi- 0.35600 grams per square inch of surface exposed.

Other modes of employing inhibitors of the class hereinbefore set forth in the acid pickling of metals are apparent to those skilled in the art to which this invention pertains. The products described additionally may be employed in the presence of foaming agents, ionizable substances or other materials ordinarily used, and are employable with the various acids commonly employed commercially in the acid pick- 1 ling of metals.

What is claimed is:

1. A process of pickling a metal which comprises subjecting the metal to be pickled to the action of a substantially nonoxidizing mineral acid solution containing a small proportion of an acid derivative of a reaction product of a thiourea and an aldehyde-ammonia.

2. A process of pickling a metal which comprises subjecting the metal to be pickled to the action of a substantially nonoxidizing mineral acid solution containing a small proportion of an acid derivative of a reaction product of a thiourea and an aliphatic aldehyde-ammonia.

3. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of an acid derivative of a reaction product of a thiourea and an aldehydeammonia.

4. A process of pickling iron and steel products which comprises subjecting the 5. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of a sulfuric acid derivative of a reaction product of a thiourea and an aliphatic aldehyde-ammonia.

6. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of a sulfuric acid derivative of a reaction product of thiocarbanilide and an aliphatic aldehyde-ammonia.

7. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of a sulfuric acid derivative of a reaction product of thiocarbanilide and acetaldehyde-annnonia.

8. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of a product formed by reacting substantially one molecular proportion of thiocarbanilide with substantially two molecular proportions of acetaldehyde-ammonia and further reacting the product thus formed with substantially one molecular proportion of sulfuric acid.

9. A pickling bath for metal products which comprises a substantially non-oxidizing mineral acid solution containing a small proportion of an acid derivative of a reaction product of a thiourea and an aldehyde-ammonia.

10. A pickling bath for metal products which comprises a substantially non-oxidizing mineral acid solution containing a small proportion of an acid derivative of a reaction product of a thiourea and an aliphatic aldehyde-ammonia.

11. A pickling bath for iron and steel products comprising a sulfuric acid solution containing a small proportion of an acid derivative of a reaction product of a thiourea and an aldehyde-ammonia.

12. A pickling bath for iron and steel products comprising a sulfuric acid solution containing a small proportion of an acid derivative of a reaction product of a thiourea and an aliphatic aldehyde-ammonia.

13. A pickling bath for iron and steel products comprising a sulfuric acid solution containing a small proportion of a sulfuric acid derivative of a reaction product of a thiourea and an aliphatic aldehydeammonia.

14. A pickling bath for iron and steel products comprising a sulfuric acid solution containing a small proportion of a sulfuric acid derivative of a reaction product of thiocarbanilide and an aliphatic aldehyde-ammonia.

15. A pickling bath for iron and steel products comprising a sulfuric acid solution containing a small proportion of a sulfuric acid derivative of a reaction product of thiocarbanilide and acetaldehyde-ammonia.

16. A pickling bath for iron and steel products comprising a sulfuric acid solution containing a small proportion of a product formed by reacting substantially one molecular proportion of thiocarbanilide with substantially two molecular proportions of acetaldehyde-ammonia and further reacting the product thus formed with substantiallv one molecular proportion of sulfuric acid.

17. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of an acid derivative of a reaction product of an aryl substituted thiourea and an aliphatic aldehyde-ammonia.

18. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of an acid derivative of a reaction product of a di-aryl substituted thiourea and an aliphatic aldehyde-ammonia.

19. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of a sulfuric acid derivative of a reactionproduct of an aryl substituted thioureav and an aliphatic aldehyde-ammonia.

20. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of a sulfuric acid derivative of a reaction product of a di-aryl substitute thiourea and an aliphatic aldehyde-ammonia containing less than eight carbon atoms.

21. A pickling bath for iron and steel products comprising a sulfuric acid solution containing a small proportion of an acid derivative of a reaction product of an aryl substituted thiourea and an aliphatic aldehyde-ammonia.

22. A pickling bath for iron and steel products comprising a sulfuric acid solution containing a small proportion of an acid derivative of a reaction product of a diaryl substituted thiourea and an aliphatic aldehyde-ammonia.

23. A pickling bath for iron and steel products comprising a sulfuric acid solution containing a small proportion of a sulfuric acid derivative of a reaction product of an aryl substituted thiourea and an aliphatic aldehyde-ammonia.

24. A pickling bath for iron and steel 252. CGMPOSITIONS,

aldehyde-ammonia containing less than eight carbon atoms.

In testimony whereof we hereunto afiix our signatures.

GEORGE L. MAGOUN. DEAL H. TOMPKINS.

Examim 

